Cladding apparatus and method

ABSTRACT

The inventions disclosed by this application are for a cladding apparatus, a cladding head, and a method of cladding a relatively planar solid object such as a boiler waterwall. Cladding of non-horizontal surfaces is complicated by the effects of gravity as melted clad material trends to runoff the surface before the cladding material bonds to the appropriate location. The disclosed inventions overcome these limitations by controlling the relative angle of application by either rotating the workpiece or the cladding head through a pre-programmed sequence. Also presented in a compact design for a laser cladding head that facilitates such cladding by minimizing movement of the laser fiber and improves cladding speed over irregular shaped objects.

Embodiments disclosed herein may be used to add alloy cladding to theexterior of relatively planar solid structures such as boilerwaterwalls. Whereas cladding a flat sheet of metal, laying in thehorizontal position, is relatively simple, the ability to clad non-flatstructures such as waterwall is enhanced through application of theapparatus and method disclosed herein. Cladding of boiler waterwallspresents a challenge as a portion of each boiler tube extends outwardfrom what would otherwise resemble a flat sheet of metal. Such astructure contains features (surfaces) with points whose tangents arenot horizontal (when the structures are laid flat). Claddingnon-horizontal structures is more difficult as gravity may causecladding material to run and not bond to the appropriate location.

Combustion units such as boiler and furnaces combusting coal or refusemay experience issues with corrosion. Use of nitrogen oxide (NOx)reduction strategies often require combustion in low excess oxygenenvironments that result in corrosive conditions. Cladding the boilerwaterwalls with alloys is an efficient method of controlling corrosionunder such circumstances.

This application presents embodiments of a cladding apparatus thatfacilitates efficient application of alloy cladding to structures whichhave raised or sloped features such as waterwalls. This application alsodiscloses a compact cladding head with features that enhance the abilityto clad irregularly shaped solid bodies. Also presenting within thisapplication are methods of efficiently cladding such structures usingthe apparatus disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conceptual isometric side view of the cladding system.

FIG. 2 shows a conceptual isometric side view of the motion system.

FIG. 3 shows a front view of a waterwall secured within the claddingsystem.

FIGS. 4A and 4B shows the front views of the cladding system with thewaterwall when they are in the tilted position.

FIG. 5A shows a conceptual model that demonstrates the initial, middle,and final positions of the cladding head using a pendulum scanner. FIG.5B shows a side view of a pendulum scanner.

FIG. 6A shows a conceptual model that demonstrates the initial, middle,and final positions of the cladding head using a virtual pivot point.

FIG. 6B shows a conceptual model that demonstrates shifting of virtualpivot points as cladding head moves from a tube to a valley.

FIGS. 7A and 7B shows two side views the cladding device and head.

FIG. 8 shows a sectional side view of the cladding device.

FIGS. 9A and 9B show the initial best mode sequence for cladding the twooutermost tubes in a boiler waterwall.

FIGS. 10A and 10B, show the subsequent best mode steps for cladding thetwo outermost tubes in a boiler waterwall. FIG. 10C demonstrates all thevarious passes taken to complete cladding the two outer walls on eitherside of the waterwall panel.

FIGS. 11A and 11B show the best mode sequence for cladding the remainderof the valleys and peaks in the horizontal position.

FIGS. 12A and 12B show the subsequent best mode sequence for claddingthe remainder of the sides while at an angle to the horizontal position.

DETAILED DESCRIPTION

Parts List

-   Cladding process system 100-   Rotary table 110-   Rotary table axis 120-   Gantry 130-   Gantry supports 150-   Carriage 160-   Main rotary 170-   Horizontal slide 180-   Track 190-   Vertical slide 210-   Cladding head 220-   Waterwall 300-   Waterwall tube 305-   Rotary table backbone 310-   Backbone face 320-   Backbone blade 330-   Clamp 340-   Pendulum scanner 500-   Torch 510-   Oscillating axis 520-   Initial virtual pivot point 610-   First layer of clad 620-   Second virtual pivot point 630-   Second layer of clad 640-   Cladding head rotation point 650-   First cladding head rotation arc 660-   Second cladding head rotation arc 670-   Optical center weaver 700-   Laser beam 720-   Beam bender 740-   Motor 750-   Focusing module 760-   Laser fiber 770-   Mirror 780-   Base metal 800-   Valley 810-   Inside peak 820-   Outside tube peak 830-   Single bead 910-   Inside side weave 920

Cladding is a welding process where another metal is metallurgicallybonded on top of a base metal. The cladding process results in a thinlayer of a pure metal on top of a transition zone containing both theclad material and the base material, followed by a layer of pure basematerial. The metallurgical bond is formed within the transition zone.Cladding of irregularly (non-flat) surfaces presents various challengesand opportunities. Cladding, as is welding, is most easily done on aflat surface with cladding applied in the direction of gravity.Irregular shaped surfaces, such as boiler waterwalls, are difficult toclad as many surfaces are sloped, resulting in potential run-off of thecladding material. The apparatus and methods described herein addressthese issues and provides for high quality, lower cost cladding ofirregularly shaped, relatively planar metals structures. Relativelyplanar solid structures are defined herein as including objects such assheet metal or panel, whether rectangle or other shape, that has anaverage length and width that is substantially greater than the averagethickness or depth. As defined herein, relatively planar solidstructures also include “panel shaped” structures with features thatextend outside the plane. For examples, as defined herein, boilerwaterwalls are relatively planar even though the waterwall panel iscomprised of a series of tubes and has features that extend outside astrict plane. Waterwalls are made of a series of tubes that areconnected to form a structure with the shape of a panel, generally flat,with a length and width component that is generally much greater thanthe thickness. Protrusions from each side of the panel, in the directionof the width may be in the form of a half tube shaped semi-circle, suchas the case with waterwalls. Similarly, this apparatus and method may beused to clad structures with protrusions having another geometric shape,including but not limited to triangles, rectangles, etc. The salientpoint in defining a relatively planar structure is that the width andlength dimensions of the structure is large in comparison to the widthand that the relatively planar structure is stable when laid on a flatsurface. Any structure that could be used to create a wall, floor orceiling (such as corrugated metal or boiler waterwalls) would beconsidered to be relatively planar.

Boiler waterwalls are comprised of a series of parallel boiler tubesthat are equally spaced, with the outer wall of each tube connected tothe outer wall of another tube with a metal strip, such that the seriesof tubes and strips form a panel. In practice, hot (and often) corrosivegasses pass on one side of the panel, transferring heat to the tubes andultimately to water within the interior of the tube to create steam.

Specific cladding materials, such as alloys, are selected for desiredproperties such as corrosion or erosion resistance. Boiler waterwallsare typically clad with nickel-based chromium alloys. As alloys can bevery expensive, an economic advantage exists for the production of cladmaterials with relatively thin alloy thicknesses. Heat exchangeequipment, thinly clad with alloys for corrosion resistance, have anadditional advantage over thickly clad materials as alloys are oftenpoor conductors of heat. The apparatus and methods described hereinaddress these specific issues by producing clad layers as thin as 0.025inches. Further, due to the low heat input associated with this claddingapparatus and method, the transition zone can be minimized to as littleas 0.002 inches with a minimal heat affected zone. A small heat affectedzone results in a stronger metal.

Information presented herein is divided into three basic subjects: themotion system, the weave technique, and the cladding head. The motionsystem includes such components as the gantry 130, carriage 160, andtrack 190. The primary objective of the motion system is to place thecladding head 220 in a desired position relative to the object to beclad. Once the cladding head 220 has been placed in the desiredlocation, the weave technique is a function of the manner in which thecladding head 220 is moved and melting energy is applied to clad in aseries of lines that result in cladding a strip. Two mechanicalembodiments that control cladding head movement and positioning thataffect weave technique are presented herein: a pendulum scanner thatproduces an oscillating side-by-side motion and a virtual pivot pointsystem that combines motion along a gantry 130 coupled with a rotatingmotion. The virtual pivot system can also mimic the side-by-side motionproduced by the pendulum scanner. Finally, information presented hereinincludes two basic cladding head configurations, an in-line claddinghead and an optical center weaver 700.

Reference is made to FIG. 1 which illustrates a conceptual model of themotion system associated with the cladding process system 100. Thisembodiment of the system is comprised of a support surface, referredherein as the rotary table 110, to support, hold, and orient a relativeflat or planar object below a movable gantry 130 that holds, supports,and moves, as needed, a cladding head 220. There is a carriage 160 thatmoves on the gantry 130, as needed. The cladding head 220 is attached tothe carriage 160 along with the main rotary 170, the horizontal slide180 and the vertical slide 210. The rotary table 110 may be tilted, asdesired around a rotary table axis 120. A gantry 130 is mounted on thetop side of the rotary table 110. It is elevated above the rotary table110 by gantry supports 150. The gantry supports 150 are attached to thetop side of the rotary table 110 via a track 190. The connection betweenthe gantry support 150 and the track 190 is designed to allow controlledmovement of the gantry 130 along the length of the rotary table 110. Theconnection between the gantry support 150 and the gantry 130 generallyforms a right angle and the resultant elevation of the gantry (relativeto the rotary table) may be fixed or alternative may be variable. Acarriage 160 is connected to the gantry 130 so as to allow controlledmovement of the cladding head 220 along the length of the gantry 130.

The carriage 160 is connected, directly or indirectly, to the mainrotary 170. The main rotary 170 allows for maintaining the horizontalslide 180 in a controlled perspective, often relative to the horizon, byallowing movement of the horizontal slide 180 around that a rotary pivotpoint. In other embodiments, it may be desirable for the horizontalslide 180 to maintain a different perspective angle than parallel to thehorizon. As mentioned previously, the rotary table 110 may be tiltedaround the rotary table axis 120. The main rotary 170 allows formaintaining the horizontal slide 180 at the desired angle relative tothe horizon irrespective of the angle of the rotary table 110. As aresult, the main rotary 170 allows control of the relative claddingangle, so that cladding can be performed at a desired angle relative tothe surface of the workpiece; often it is desired to clad in thedirection of gravity.

Referring now to FIG. 2 which shows further available range of motion inthe conceptual model. The gantry 130, which lies above and parallel tothe rotary table 110, is connected to a carriage 160, which hascontrolled movement along the length of the gantry 130. The horizontalslide 180 is connected to the carriage 160 via the main rotary 170,allowing control of the angle formed between the carriage 160 andhorizontal slide 180. Attached to the horizontal slide 180 is thevertical slide 210 and the cladding head 220. The cladding head 220 isconfigured to have movement so as to allow cladding a line on aworkpiece.

Reference is made to FIG. 3 which illustrates a more detailed front viewof the cladding process system 100. FIG. 3 illustrates that the rotarytable 110 may consist of a series of rotary table backbones 310 thatsupport the workpiece, in this embodiment a boiler waterwall 300. Inthis embodiment, a series of rotary table backbones 310, consideredtogether, form a rotary table 110. The rotary table 110 is formed byconfiguring the series of rotary table backbones 310 such that eachbackbone face 320, shown as a triangle in FIG. 3, fall into a plane thatis parallel to the planes encompassing other backbone faces 320, therotary table axis 120 passes through the center of each backbone face320 and waterwalls 300 lay flat on the top of each backbone blade 330.The rotary table backbones 310 may be of different sizes, thickness andspacing with such dimensions only dependent on that which is required tosupport the object to be clad. The object to be clad, in this embodimentis a boiler waterwall 300 which is held down and secured with a clamp340. Other securing embodiments known to person's knowledge of fasteningtechnology may be employed. The rotary table 110 is modular. Rotarytables 110 of the same width can be joined together for longerwaterwalls 300.

Continuing with FIG. 3, the cladding process system 100 is comprised ofcomponents previously identified in FIGS. 1 and 2. Gantry supports 150,are secured to a track 190, and support a gantry 130. A vertical slide210, along with the cladding head 220 are connected to the gantry 130via a carriage 160 coupled with a main rotary 170 (not shown) and ahorizontal slide 180. As discussed previously, the combined effect ofthe motion system allows for the cladding head 220 to be place above theobject to be clad across the entire area of the rotary table 110.Although not shown in the figure, cooling water (approximately 100-110°F.) is circulated through the tubes in the panel during the claddingprocess to control and maintain the temperature of the base metal tooptimize the weld. Every tube has a parallel line from the watermanifold.

Experience has shown that, where possible, it is highly desired to cladin the direction of gravity. Such is commonly referred to as the 1Gposition (which means perpendicular to the ground +/−15°). In oneembodiment, the rotary table system 110 can be used to clad boilerwaterwalls 300. In other embodiments, the rotary table system can beused to clad other generally planar objects with or without varyingprotrusions from the plane. Waterwalls are made of a series of tubesthat are connected to form a structure with the shape of a panel,generally flat, with a length and width component that is generally muchgreater than the thickness. Protrusions from each side of the panel, inthe direction of the width may be in the form a half tube shapedsemi-circle, such as the case with waterwalls 300.

FIG. 3, which utilizes a pendulum scanner 500, illustrates the abilityto directly clad only a limited portion of the the top surface of thetubes 305 from the 1G position when the rotary table 110 is in thehorizontal position. Other portions of the tube may not be clad directlyin the direction of gravity when the rotary table 110 is horizontal asshown in FIG. 3. Although not depicted in FIG. 3, the weave could alsobe achieved by utilizing a virtual pivot point as illustrated in FIGS.6A and 6B.

Now presenting FIGS. 4A and 4B, which are identical to FIG. 3 exceptthat the rotary table 110 is rotated around the rotary table axis 120(no longer horizontal). Rotation of the rotary table 110 around therotary table axis 120 coupled with rotation of the cladding head 220around the main rotary 170 allows for direct placement of the claddinghead 220 above other portions of the tube 305 and allows for claddingfrom the 1G position.

Various weaving techniques may be incorporated into the disclosed deviceand methods. This includes a linear weave, pendulum weave, virtual pivotweave, and weave shaping. Linear weaves simply involve laying lines ofclad through movement of the cladding head 220 along the gantry 130 orhorizontal side 180 without any other motion (such as the oscillatingmotion of the pendulum scanner). FIG. 5A conceptually presents thependulum weave technique using a pendulum scanner 500. This figureillustrates that the vertical slide 210 is located just about the centerof the tube (highest part of the curve) and the cladding head 220 sweepsfrom left to right to clad a line across the top of the top of the tube.When cladding other portions of the tube, the vertical slide 210 and thecladding head 220 are positioned overtop of the section of the workpieceto be clad. As a result, the working distance from the focus lens in thefocusing module 760 (discussed later) to the point being clad is notnecessarily the same at all points of the weave. At the end of theweaves, the cladding material melts before it touches the tube surface.

The pendulum scanner 500 produces the side-by-side sweeps via anoscillating motion of the pendulum scanner oscillating axis 520. Thisoscillating motion is accomplished by partially rotating the oscillatingaxis 520 around its center in one direction followed by an equivalentpartial rotation around its center in the other direction. FIG. 5B showsthe pendulum scanner 500 and its oscillating axis 520, and demonstrateshow this motion induces a side-by-side sweeping motion of the torch 510.Since the torch 510 is a part of the cladding head 220, the inducedmotion of the torch 510 causes a side-by-side motion of the claddinghead energy source (e.g. a laser) that melts cladding material deliveredby the torch 510; the two move together. The oscillating motion producesa side-by-side motion of both the torch 510, which is a claddingmaterial delivery device, and the energy source for melting the claddingmaterial (e.g. a laser) in unison.

After cladding a line, the motion system instructs the carriage 130 tomove the cladding head 220 incrementally in the direction of bare(unclad) metal and the sweeping process, now likely right-to-leftcontinues. This sequence of cladding a line and moving the cladding head220 is repeated until the entire length of a tube is clad. Aftercladding a particular portion of the workpiece, the vertical slide 210travels and orients the cladding head 220 over a different portion ofthe workpiece and the process is repeated. When cladding waterwalls,peaks, valleys and sides may be clad as individual passes. This processis repeated until all desired portions of the surface of the workpieceare clad.

The motion of the gantry 130 along the track 190 coupled with the motionof the cladding head 220 results in cladding a strip along the length ofthe workpiece. The width of the strip can be controlled to be as smallas required; the “strip” can be a single bead (line) by eliminating theside-by-side oscillation. The weave width can be increased as long asthe cladding material hits the melting energy (e.g. laser beam 520) justabove the tube surface.

FIG. 6A conceptually presents a weave technique using a virtual pivotpoint. This figure demonstrates three separate but coordinated motionsto facilitate placing the cladding head 220 just above and perpendicularto the tangent line to any surface of the workpiece. In summary, thecladding head 220 rotates and rises and falls as it travels across thelength of the gantry 130.

The first figure (to the left) demonstrates the relative position of thecladding head 220 to a tube at the beginning the weave. Here thecladding head 220 is directed toward the furthest practical downsideslope of the tube. Unlike the pendulum scanner, utilization of a virtualpivot point will often result in the cladding head 220 operating in anon-vertical position. As the tube is clad, from left-to-right, thevertical slide 210 will travel from left-to-right along the gantry 130or the horizontal slide 180 and the cladding head 220 will rotate in acoordinated manner so as to maintain the cladding head, nearly aspractical, perpendicular to the tangent line of the tube (at the pointof cladding). The middle figure illustrates that when the center of thetube is reached, the cladding head 220 is pointing straight down in thedirection of gravity and cladding the very top of the tube. The verticalslide continues to travel to the right and the cladding head 220rotates, still pointing to the virtual pivot point, to maintain thedirection of cladding at an angle perpendicular to the tangent line ofthe surface of the tube at the point of application. Unlike the pendulumscanner 500, the working distance from the focus lens in the focusingmodule 760 to the point being clad remains relatively constant at allpoints of the weave when cladding in-line with the virtual pivot point.

The virtual pivot point is not static and will move from time to timebased on the topography of the surface being clad. The virtual pivotpoint is not to be confused with the point of rotation for the claddinghead 650. In these embodiments, the claddings head 220 is attached to avertical slide 210; whereas the cladding head 220 may be configured torotate around a fixed point associated with the vertical slide 210, thismay or may not be the virtual pivot point.

This concept is demonstrated in FIG. 6B. Considering the figure fromleft to right, the initial virtual pivot point 610 is located in thecenter of the tube. As the cladding head travels from left to right (dueto motion along a gantry 130 or horizontal slide 180, not shown), thecladding head 220 must rotate around the cladding head rotation point650 to maintain the direction of cladding so that it is perpendicular tothe tangent of the tube surface at that point. That said, in thisexample, the cladding head 220 is always pointing at the center of thetube (i.e., the first virtual pivot point 610) until it approaches thevalley (or membrane). However, in order to maintain a relativelyconstant distance between the cladding head 220 (especially the end ofthe torch 510) and the surface of the workpiece, the cladding head 220may rise and fall vertically based of movement of the vertical side 210(not shown). Making a single weave (line), while directing the claddinghead constantly at a single virtual pivot point requires threesimultaneous motions: generally horizontal movement of the cladding head220 along the gantry 130 or horizontal slide 180, rotation of thecladding head 220 around a cladding head rotation point 650, andvertical movement, as needed to maintain a relatively constant distancebetween the cladding head 220 and the workpiece, along the verticalslide 210. When combined, these three motions result in motion of thecladding head rotation point 650 through the first cladding headrotation arc 660. While pivoting around the first pivot point 610, acontinuous layer of clad 620 is laid across the top of a tube.

Sometime prior to reaching the valley 810, the virtual pivot point mustshift to another location, this time a second pivot point 630, locatedat a point in space above the valley 810. Although this point may beclose to the cladding head rotation point 650, they are not necessarilythe same. In this example, the horizontal motion ceases (or is minimal)and the cladding head 220 pivots through a second pivot point 630 byrotating and moving the cladding head rotation point 650 through thesecond cladding head rotation arc 670, resulting in a continuous layerof clad 640 above a valley 810.

At this point, the cladding head 220 is in the exact same position aspreviously described, but in reference to the adjacent tube. Claddingwith this approach can result in a continuous clad across the entireworkpiece; to be successful, the switch of virtual pivot point mustoccur at a location where the resultant clad would be a part of thefirst arc of clad on top of the tube 620 and part of the second arc ofclad in the valley 640. To be of greatest benefit, the switching ofpivot points must occur without cessation of cladding and the “twoclads” must be seamless.

After cladding a line, the motion system instructs the carriage 130 tomove incrementally in the direction of bare (unclad) metal and theprocess of rotating the cladding head 220 and moving the vertical slide210 is repeated. This could be accomplished by reversing direction witha right-to-left motion, or returning back to the left and cladding in aleft-to-right motion. This sequence of cladding a line and moving thecladding head 220 is repeated until the entire length of a tube is clad.After cladding a particular portion of a tube, the cladding head 220travels to another portion of a tube and the process is repeated. Thisprocess is repeated until all desired portions of the surface of theworkpiece are clad.

Considering the motion of the gantry 130 along the length of the track190, the generally horizontal (or widthwise) movement or the carriage160 along the length of the gantry 130, coupled with the pivoting motionaround the virtual pivot point, the cladding process system creates astrip of clad alloy along the length of the workpiece. The width of thestrip can be controlled to be as small as required; it could be a singlebead or line. In this embodiment, the maximum width, when claddingaround a single virtual pivot point is limited by the presence of theadjacent tube or an inflection in the surface of the structure.

The maximum width can be the entire width of the workpiece if multiple(and shifting) virtual pivot points are used and the peak, valleys andsides are clad as one continuous pass. In that embodiment, the workpieceis clad across its entire width. As such, the vertical side could travelfrom one end of the gantry 130 to the other end of the gantry 130 in onewidthwise motion; the cladding head 220 would pivot, as needed tomaintain the head alignment perpendicular to the surface being clad.

Cladding in positions other than 1G is possible, but more difficult.Embodiments disclosed herein include weave shaping techniques whichinclude laser beam spot shape control, laser beam power modulation, andlaser beam stirring. Laser beam power modulation which is accomplishedby varying the laser power in time by amplitude or pulse widthmodulation (“PWM”). Use of these techniques allows varying the strengthof the laser at different points of the weave (lower power at the endscompared to the center of the weave). These techniques reduce the amountof energy input into the cladding material (compared to cladding at 1G)resulting in less melt mass per unit time. Where welding/cladding isbeing performed on a sloped surface, as demonstrated in the left andright figures in FIG. 6, energy modulation allows for proper bonding tooccur on sloped surfaces by preventing cladding material from runningtoo quickly down the sloped surface. Said another way, modulation of theenergy input to the cladding material results in less energy input permass per time, less melting mass per time, resulting in shorter andsmaller puddles of melted clad material, allowing for surfaceattractions to overcome the effects of gravity, holding these smallpuddles in place long enough to bond. In addition, uses of laser beammodulation can help to induce a stirring effect that decreases potentialdefects in the weld. The left and right multi-G examples are contrastedagainst the center figure which is performed at the 1G position. Use ofenergy modulation techniques can minimize or eliminate the need forwelding in the 1G position, or otherwise can increase the speed ofcladding when in the 1G position.

Additional control of the welding/cladding process can be achievedthrough laser beam spot shape control where the round laser spot istransformed to an oval spot or other geometry. This is accomplished byusing alternate optics in the cladding head to shape the beam. Forexample, an oval is created with a cylindrical lens. Segmented opticallens or diamond turned facets can be used to create beam spot patterns.This can help by improving the shape of the molten puddle; the heat flowout of the molten zone may require more heat on the sides of the beamrather than adding up to high in the center.

Another technique that can be used to improve the clad or weld is laserbeam stirring. This technique requires using a smaller laser beam tofill out a larger spot or shape at a high speed such that it stirs themolten puddle. This may improve the weld or clad by slinging outinclusions or potential defects. Stirring helps to bring slag to the topof the puddle rather than disturb the bond interface.

FIG. 7A illustrates a side view of a laser cladding device. Lasercladding devices may operate with an in-line cladding head, or asillustrated in FIGS. 7A, 7B and 8, may operate as an optical centerweaver 700. The in-line device operates just as the term describes; alaser energy is received from a laser fiber 770 which is connected tothe top of the device (which is in the shape of a tube) and the energypasses “in-line” until it exits at the bottom (where it intersects withthe cladding material delivered by the torch 510). A water cooled fiberoptic cable delivers the laser beam (from its source) to the headthrough the fiber. The energy leaving the laser fiber is focused by alens (in this example a water cooled bi-convex lens) located within thefocusing module 760, resulting in a focused, high-energy beam 720 thatis projected to the base clad surface where it meets the claddingmaterial delivered by the torch 510.

The optical center weaver 700, illustrated in FIGS. 7A, 7B, and 8, hasall the same features as the in-line except it has a beam bender 740 anda motor 750. The beam bender 740 is adjustable and water cooled and hasa highly reflective mirror 780 that reflects the laser beam on to theclad surface at a set angle. The motor 750 facilitates a side-by-sidemotion (similar in results to the pendulum scanner as shown in FIG. 5A);alternatively optical centered weaver may operate using a pivot motionin unison with the vertical and horizontal slide (as illustrated in FIG.6). The motor 750 is used to used to move the mirror 780 in such a waythat the focused laser beam 720 dithers from side to side resulting in aline. In one embodiment, a digitally controlled Servo motor is used torotate the mirror sufficiently to cause the laser point to move acrossthe workpiece. Unlike the pendulum scanner, this side-by-side motion canbe achieved, forming a line of clad with the optical centered weaver 700without otherwise moving the cladding head 220.

This embodiment also incorporates a torch 510 that is attached in afixed position into the optical centered weaver 700. The torch 510 is ahollow cylinder shaped cladding material delivery and heating device.The outlet of the torch 510 is in a fixed position such that thecladding material leaving the torch 510 intersects with the laser beam720 just above the surface to be clad. As a result, the optical centeredweaver 700 could be portable, that is not connected to a claddingprocess system 100 as described previously. When cladding with theoptical centered weaver 700, any surface on any object can be clad ifmeans exist to position the end of the cladding head above the surfaceof the workpiece such that the laser beam 720 intersects with thecladding material (delivered by the torch 510) just above the surface ofthe workpiece and melting energy is modulated as needed to account forirregular shapes and slops and weaving speed.

The optical center weaver 700 has two additional advantages over anin-line cladding head. First, given the configuration and the desiredmotions, the position of the laser fiber remains relatively constantwhen compared to the in-line cladding head, especially when coupled withcladding around a virtual pivot point. Secondly, the motor facilitatesmuch faster weaving speeds since the optical center weaver 700 hasgreater capability in reaching and cladding sloped surface withoutstopping to make positional adjustments (e.g., wider strips, fasteroscillations).

In the embodiment presented in FIGS. 7A and 7B, the cladding material isa hot wire that is melted by laser fusion. Other process embodiments areavailable such as cold wire or powder laser fusion, hot or cold wire orpowder laser key hold welding, combinations or wire and powder, andlaser hybrid welding where the laser beam and the electrical arc actsimultaneously on the same weld puddle). Lasers incorporated in thecladding process system can include fiber lasers, diode lasers, fiberdelivered diode lasers and carbon dioxide lasers. Optics associated withthe laser could be refractive, reflective, or diffractive.

The embodiment presented in FIGS. 7A and 7B utilize hot wire as acladding material. In this embodiment, hot wire is heated as it passesthrough the torch 510 via AC (alternate current) electrical resistance.Other heating embodiments include electrical resistance heating via DC(direct current) heating or pulsed heating, radio frequency, smallfurnace, plasma, optical, laser, or a hybrid of any other previouslymentioned heating methods.

Returning to FIGS. 7A and 7B, heated wire is fed through the torch 510so that the hot wire intersects the laser beam 720 just above the pointto receive the cladding material. The hot wire may be heated to theplastic point so that the energy requirements to melt the wire with thelaser are minimized. Otherwise, the cladding material (wire or powder)may be cold or partially heated. The hot wire feeder and the laser beamare configured to move together in unison giving the device a compactdesign; the wire and the beam stay together as the cladding head 220moves.

Now presenting FIG. 8, which illustrates a side sectional view of theoptical center weaver 700. Consistent with FIGS. 7A and 7B, a laser beamis shot down the center of the optical center weaver 700 to the mirror780 that redirects the laser beam to a common point where the hot wireis delivered by the torch 510. A clear advantage of the disclosed deviceis the compact design, combining the laser source and beam and cladmaterial feeder and keeping the hot wire and beam together despitemanipulation of the cladding head. The optical center weaver 700, asdisclosed herein, allow for optimal beam shaping and scanning, with beamcenter rotation.

FIGS. 9 through 12 demonstrate one example of the “weaving” process usedto clad a waterwall where the entire workpiece is clad via a series ofstrips. Cladding strips, as described below, may be laid down throughuse of an in-line or optical center weaver 700, coupled with either apendulum scanner or a virtual pivot. Alternatively, a workpiece can beclad by using the vitural pivot method with or without rotation of thetable and workpiece. In these examples, a series of strips and beads ofclad are laid on the workpiece so that the area to be clad is fullycovered. These strips and beads are laid adjacent to one another with asmall overlap to assure continuity of the cladding and when combined,result in a continuous layer of cladding. In another example of weaving,the entire width of the workpiece can be clad as described previouslyutilizing a virtual pivot point.

FIG. 9A illustrates the first steps in the clad sequence to clad thebase metal 800 on and between the outermost two adjacent tubes on oneside of a waterwall 300 through cladding a series of strips. Aftersecuring the waterwall 300, the first step is to clad the valley 810between the two outermost tubes followed by cladding the inside peak 820on the second outermost tube with the rotary table 110 in the horizontalposition (as shown in FIG. 3). Cladding of the valley 810 and the insidepeak 820 can be accomplished in the 1G position when the rotary table110 is in the horizontal position. The entire width of the valley 810 isclad as a result of the side-to-side movement of the cladding head,previously described. The entire length of the valley is clad as aresult of the movement of the gantry 130 along the entire length of thetrack 190. The entire length of the cladding on the inside peak 820 isapplied by the same motions described for the valleys 810.

Step 2 is presented in FIG. 9B. After the cladding is laid down asindicated in FIG. 9A, the rotary table 110 is tilted between 10°-75°with a preferred angle of between 10°-14° with a best mode beingapproximately 12°. Cladding is now applied to the outermost tube peak830 in such a way that it reaches between the 1-3 o'clock positions,with the best mode being 2 o'clock while maintaining the same wireheight on both sides of the weave. The wire should hit the laser beamjust above the clad surface. Cladding of this portion of the outsidetube could fall just outside a 1G position.

Step 3 is presented in FIG. 10A. After the cladding is laid down asindicated in FIG. 9B, the rotary table 110 is tilted between 10°-75°with a preferred angle of between 35°-45° with a best mode beingapproximately 40°. Also see FIG. 10A for reference. Here a first bead910 is laid down at the point that the valley 810 meets a tube locatedon the down slopping side wherein half of the single bead should be onthe edge of the corresponding valley. The bead 910 is an importantfeature of the weaving sequence as it improves the tie between thevalley 810, the second inside weave 920 (discussed below) and the basemetal. The bead 910 is clad down the entire length of the waterwall.Rotation of the table, as described herein, allows for the bead 910 tobe laid down from the 1G position.

Step 4 is presented in FIG. 10B. The rotary table 110 is tilted between10°-75° with a preferred angle of between 40°-50° with a best mode beingapproximately 45°, results in a tube surface capable of cladding in the1G position. After the cladding is laid down as indicated in FIG. 10A,the first inside weave 920, located adjacent to the first bead 910, isclad down the entire length of the waterwall 300.

Following cladding of the first inside weave 920, the rotary table 110is tilted in the other direction between 10°-75° with a preferred angleof between 35°-45° with a best mode being approximately 40°. Also seeFIG. 4B for reference. A second bead 910 is laid down at the point thatthe valley 810 meets a tube on the (now) down slopping side, followed bya second inside weave 920 as was performed previously when the table wastitled in the other direction. FIG. 10C illustrates the cladding onadjacent tubes as clad in the above sequence.

Although the clad sequence could vary and produce an equivalent product,FIGS. 11A and 11B coupled with FIGS. 12A and 12B illustrates the bestmode for cladding the remainder of the valleys and peaks (in thehorizontal position) and the remainder of the sides (while at an angleto the horizontal position). First, all of the valleys 810 are clad, oneafter another, going left to right, or right to left. After all thevalleys 810 are clad, all the peaks 820 are clad in the oppositedirection as indicated in FIG. 11B. FIG. 12A illustrates that next, allthe downside linear beads 910 and inside weaves 920 are clad in sequencewhen the rotary table 110 is tilted in one direction, and that the otherdownside linear beads 910 and inside weaves 920 are clad in sequencewhen the rotary table 110 is tilted in the other direction. The stepsdiscussed herein are used to clad the remainder of the panel.

The clad sequence described herein relates directly to cladding anobject with the layout of boiler waterwalls 300. This sequence reflectsan optimal solution by minimizing the time required to clad thewaterwall 300. Time minimization is accomplished by minimizingnon-cladding time and movement. Other equivalent or near equivalentsequences may exist. For example, the waterwall could be produced bycladding left-to right (or right-to left), alternately cladding insidepeak—valley—inside peak—valley, etc, rather than sequentially claddingall the valleys 810 followed by all the inside peaks 820. Such analternate sequence example is disclosed herein, however has thedisadvantage of additional setup time and panel distortion. Otherexamples would include any permutations associated with cladding theidentified sections of the waterwall 300.

The apparatus and method described herein has multiple moving parts andrequires implementation of steps in pre-planned and coordinated fashion.For example, in laying down a strip of clad, it is necessary tocoordinate successive lying down of lines, followed by incrementalmovement of the gantry 130 along the track 190. Upon cladding a strip,the apparatus and method require movement of the cladding head 220 alongthe horizontal length of the gantry 130 to position the cladding head220 so as to repeat the sequence and lay another series of lines forminga strip. Under various embodiments the rotary table is rotated to exposebare metal to the 1G position. Finally, cladding around a virtual pivotpoint requires simultaneous horizontal movement of the cladding head 220along the gantry 130 or the horizontal slide 180 while pivoting thecladding head to form a different angle (to the horizon) to maintain thecladding head at a position that is perpendicular to the tangent line onthe surface being clad. All these motions require a control system withprogrammable logic to coordinate the efficient movement as describedabove. Means for such movement is accomplished through uses of gearedsystems and motors, or the equivalent, unless otherwise specified.

Considering the above disclosure, the cladding process system 100 hasseveral distinguishing features. These include a motion system toprovide cladding head 220 access, wherever possible in the 1G weldposition (in reference to the object to clad). When not possible to cladin the 1G position, the cladding process system 100 provides forcontrols, processes and method to perform multi-G welding. The claddingprocess system 100 also incorporates a control system to control, trackand monitor cladding performance in a pre-determined sequence utilizingmotion controllers, software, data collection quality reports, necessaryinputs/outputs, and a user (operator) interface, (mechanical,electrical, and/or optical) tracking systems. Finally the claddingprocess system 100 utilizes structures to hold and orient the object tobe clad (rotary table 110, rotary table backbone 310, and clamp 340).

Cladding using this device and method has the advantage of producing auniformly thin layer of cladding while minimizing the thickness of themetallurgical bond (interface). Thin, uniform cladding, minimizing theinterface has the advantage of lower cost (less expensive alloy) andstronger welds. Although thicker layers are achievable if desired,cladding thickness is always controllable to less than 0.070 inches withtypical thicknesses of 0.055 inches, with minimum thickness of 0.020inches being of within ten percent dilution of cladding alloy.

We claim:
 1. A metal cladding apparatus for cladding a workpiececomprising: a. a cladding head, wherein said cladding head has a firstend and a second end; b. wherein a laser energy is provided from a lasersource to said first end and a focus laser beam is imparted from saidsecond end to melt a cladding material; c. a cladding head motionsystem, that positions said second end of said cladding head above anddirected toward a surface of a workpiece; d. a workpiece holding devicethat has means to maintain said workpiece at a relative angle to saidfocus laser beam projected from said second end of said cladding head;e. wherein said cladding head motion system is comprised of a gantry, ameans of support for said gantry, and a track that extends along thelength of said workpiece holding device, wherein said cladding headmotion system has means to move said gantry along the length of saidtrack; wherein said cladding head is attached to said gantry and whereinsaid cladding head has means to move along the length of said gantry; f.wherein said cladding head motion system also has means to move saidfocus laser beam projected from second end of said cladding head in aside-by-side sweeping motion to produce a first line of clad on saidsurface of said workpiece; g. wherein said cladding head motion systemsubsequently moves said cladding head incrementally in a directionperpendicular to said first line of clad where a second line of clad islaid adjacent to and continuous with said first line of clad through asubsequent side-by-side sweeping motion; h. wherein further repetitionof said incremental movement of said cladding head in said directionperpendicular to said first and second lines followed by saidside-by-side sweeping motion produces a first strip of clad on saidworkpiece; i. wherein a second strip of clad is laid on an unclad areaof said workpiece through movement of the cladding head along the lengthof said gantry to said unclad location, followed by producing a firstline of said second strip of clad through said side-by-side sweepingmotions, followed by said incremental movement in a directionperpendicular to said first line of said second strip, followed byproducing a second line of said second strip through said side-by-sidesweeping motions, followed by subsequent repetitive said incrementalmovement and said cladding of lines until said second strip iscompleted; j. wherein said motion of said cladding head along the lengthof said gantry allows for cladding additional strips on said workpiecethrough repeated said side-by-side sweeping motions followed by saidincremental movement of said cladding head in said directionperpendicular to said side-by-side sweeping motions until saidadditional strips are completed; and k. a control system configured tocontrol said motion of said cladding head motion system and saidcladding head.
 2. The apparatus of claim 1 where said projection of saidfocus laser beam from said second end of said cladding device ismaintained in the 1G position.
 3. The apparatus of claim 2 wherein saidmeans to maintain said workpiece at said relative angle to said focuslaser beam projected from said second end of said cladding head is amotor that rotates said workpiece holding device to cause said focuslaser beam projected from said second end of said cladding head tointersects said surface of said workpiece at an angle that isperpendicular to a tangent line at said surface of said workpiece. 4.The apparatus of claim 3 wherein a bead of clad is laid at the interfacebetween two adjacent strips of clad by moving said second end of saidcladding head to a location above said interface between two adjacentstrips of clad and cladding said bead along the length of said workpieceby moving said gantry along said length of said track without saidside-by-side sweeping motion.
 5. The apparatus of claim 3 wherein saidworkpiece is a boiler waterwall.
 6. The apparatus of claim 3 whereinsaid cladding head is a laser source selected from the group consistingof a fiber laser, diode laser, fiber delivered diode laser, and a carbondioxide laser.
 7. The apparatus of claim 3 wherein said claddingmaterial is selected from the group consisting of powder, cold wire, andhot wire.
 8. The apparatus of claim 3 wherein means to move said secondend of said cladding head in a side-by-side sweeping motion to clad saidline on said workpiece is a pendulum scanner.
 9. The apparatus of claim3 wherein said cladding head is a laser that further comprises: a. ahollow cylinder shaped vessel that surrounds the laser energy; b. watercooled fiber optical cable that delivers said laser energy to a firstend of said hollow cylinder; c. a focusing lens, located within saidhollow cylinder, that receives said laser and focuses it; d. a mirrorthat redirects said focused laser between 30° and 120°; e. a means torotate said mirror so as to produce said side-by-side sweeping motion;f. a second end of said hollow cylinder which is located in thedirection of said redirected focused laser; g. a torch; h. wherein saidtorch heats a cladding material; i. said torch mounted in a fixedposition, wherein said heated cladding material exits said torch at apoint that intersects with said redirected focused laser.
 10. A metalcladding apparatus for cladding a workpiece comprising: a. a claddinghead, wherein said cladding head has a first end and a second end; b.wherein a laser energy is provided from a laser source to said first endand a focus laser beam is imparted from said second end to melt acladding material; c. a cladding head motion system, that positions saidsecond end of said cladding head above and directed toward a surface ofa workpiece; d. a workpiece holding device; e. wherein said claddinghead motion system is comprised of a gantry, a means of support for saidgantry, and a track that extends along the length of said workpieceholding device, wherein said cladding head motion system has means tomove said gantry along the length of the track; wherein said claddinghead is attached to said gantry and wherein said cladding head has meansto move along the length of said gantry; f. wherein said cladding headmotion system also comprises a means to maintain the focus laser beamprojected from said second end of said cladding head so that saidprojection of said focus laser beam intersects said surface of saidworkpiece at an angle that is perpendicular to the tangent of saidsurface of said workpiece; g. wherein said cladding head motion systemalso comprises a means to maintain a relatively constant distancebetween said second end of said cladding head and said surface of saidworkpiece through movement of said second end of said cladding head in avertical direction; h. wherein said cladding head motion system producesa line of clad by melting said cladding material while moving saidcladding head along said gantry while maintaining the projection of saidfocus laser beam in a direction that is relatively perpendicular to saidtangent line of said surface of said workpiece and maintaining thesecond end of said cladding head at said relatively constant distancefrom said surface of said workpiece; i. wherein a first line of clad islaid; j. wherein said cladding head motion system subsequently movessaid cladding head incrementally in a direction perpendicular to saidfirst line of clad where a second line of clad is laid adjacent to andcontinuous with said first line of clad; k. wherein a first strip ofclad on said workpiece is laid through further repetition of saidincremental movement of said cladding head in said directionperpendicular to said first and second lines followed by laying ofsubsequent lines of clad until said first strip of clad is completed; l.wherein a second strip of clad is laid on an unclad area of saidworkpiece through movement of the cladding head along the length of saidgantry to said unclad location, followed by producing a first line ofclad of said second strip, followed by said incremental movement in adirection perpendicular to said first line of clad of said second strip,followed by producing a second line of clad of said second strip,followed by subsequent and repetitive incremental movement in adirection perpendicular to said first and second lines of clad of saidsecond strip followed by cladding subsequent lines of clad until saidsecond strip is completed; m. wherein said motion of said cladding headalong the length of said gantry allows for cladding additional strips onsaid workpiece through repeated said cladding a line followed by saidincremental movement of said cladding head in said directionperpendicular to said prior line of clad; and n. a control systemconfigured to control said motion of said cladding head motion systemand said cladding head.
 11. The apparatus of claim 10 wherein said meansto maintain the focus laser beam projected from said second end of saidcladding head so that said projection of said focus laser beamintersects said surface of said workpiece at an angle that isperpendicular to the tangent of said surface of said workpiece isaccomplished through rotation of said cladding head around a point ofsaid cladding head as it travels said length of said gantry; whereinsaid means to maintain a relatively constant distance between saidsecond end of said cladding head and said surface of said workpiece isaccomplished through movement of said second end of said cladding headin a vertical direction.
 12. The apparatus of claim 10 wherein a bead ofclad is laid at the interface between two adjacent strips of clad bymoving said second end of said cladding head to a location above saidinterface between two adjacent strips of clad and cladding said beadalong the length of said workpiece by moving said gantry along saidlength of said track without said side-by-side sweeping motion.
 13. Theapparatus of claim 10 wherein said cladding head is a laser sourceselected from the group consisting of a fiber laser, diode laser, fiberdelivered diode laser, and a carbon dioxide laser.
 14. The apparatus ofclaim 10 wherein said cladding material is selected from the groupconsisting of powder, cold wire, and hot wire.
 15. The apparatus ofclaim 10 wherein said cladding head is a laser that further comprises:a. a hollow cylinder shaped vessel that surrounds the laser energy; b.water cooled fiber optical cable that delivers said laser energy to afirst end of said hollow cylinder; c. a focusing lens, located withinsaid hollow cylinder, that receives said laser and focuses it; d. amirror that redirects said focused laser between 30° and 120°; e. asecond end of said hollow cylinder which is located in the direction ofsaid redirected focused laser; f. a torch; g. wherein said torchdelivers and heats said cladding material; and h. said torch mounted ina fixed position, wherein said heated cladding material exits said torchat a point that intersects said redirected focused laser.
 16. Theapparatus of claim 10 wherein said workpiece is a boiler waterwall. 17.The apparatus of claim 10 wherein said workpiece holding device hasmeans to maintain said workpiece at a relative angle to said focus laserbeam projected from said second end of said cladding head.
 18. Theapparatus of claim 10 wherein said first line of clad is laid along theentire width of said workpiece.